U.S. patent application number 16/650959 was filed with the patent office on 2020-08-13 for method for the insertion of guilloche patterns, method for the extraction of guilloche patterns, method for the authentication o.
The applicant listed for this patent is THALES DIS FRANCE SA. Invention is credited to Mohamed BOUABDELLAH, Maxime Carre, Michel JOURLIN, Joseph LEIBENGUTH.
Application Number | 20200254807 16/650959 |
Document ID | 20200254807 / US20200254807 |
Family ID | 1000004828556 |
Filed Date | 2020-08-13 |
Patent Application | download [pdf] |
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United States Patent
Application |
20200254807 |
Kind Code |
A1 |
LEIBENGUTH; Joseph ; et
al. |
August 13, 2020 |
METHOD FOR THE INSERTION OF GUILLOCHE PATTERNS, METHOD FOR THE
EXTRACTION OF GUILLOCHE PATTERNS, METHOD FOR THE AUTHENTICATION OF
THESE GUILLOCHE PATTERNS AND DEVICES FOR IMPLEMENTATION
Abstract
A method of inserting guilloche patterns in a document, each
guilloche pattern being capable of encoding variable alphanumeric
data ensuring a different aspect at each guilloche pattern so as to
render said document secure using an operation of determining an
insertion intensity of each guilloche pattern previously generated
on the basis of a mid-gray level of the document near said
guilloche pattern. A device for implementing this insertion method.
The method further provides for extracting guilloche patterns from
a secure document likely to be degraded by determining a contrast
card of at least one portion of the secure document that includes
the guilloche patterns, identifying, on this contrast card an
optimal percolation trajectory, and extracting the optimal
percolation trajectory, said trajectory corresponding to the
guilloche pattern. The method further provides for authentication
of the guilloche patterns of a secure document likely to be
degraded, by the extraction operations, and comparing each
extracted guilloche pattern with a corresponding theoretical
guilloche pattern.
Inventors: |
LEIBENGUTH; Joseph; (Meudon,
FR) ; JOURLIN; Michel; (Meudon, FR) ; Carre;
Maxime; (Meudon, FR) ; BOUABDELLAH; Mohamed;
(Meudon, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THALES DIS FRANCE SA |
Meudon |
|
FR |
|
|
Family ID: |
1000004828556 |
Appl. No.: |
16/650959 |
Filed: |
September 25, 2018 |
PCT Filed: |
September 25, 2018 |
PCT NO: |
PCT/EP2018/075980 |
371 Date: |
March 26, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B42D 25/337 20141001;
B42D 25/309 20141001; B42D 25/305 20141001; B42D 25/23
20141001 |
International
Class: |
B42D 25/337 20060101
B42D025/337; B42D 25/305 20060101 B42D025/305; B42D 25/309 20060101
B42D025/309; B42D 25/23 20060101 B42D025/23 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 26, 2017 |
EP |
17306266.2 |
Claims
1. A method of inserting guilloche patterns in a document, each
guilloche pattern being capable of encoding variable alphanumeric
data ensuring a different aspect at each guilloche pattern so as to
render said document secure, the method comprising determining an
insertion intensity of each guilloche pattern previously generated
on the basis of a mid-gray level of the document near said
guilloche pattern and in that the insertion intensity of said
guilloche pattern involves a contrast value and a thickness of said
guilloche pattern.
2. The method of inserting guilloche patterns according to claim 1,
further comprising calculating, in each pixel of said guilloche
pattern, the contrast value between an internal area of the
guilloche pattern and an external area near said internal area.
3. The method of inserting guilloche patterns according to claim 2,
wherein the contrast value is obtained by comparing the mid-gray
level of the internal area and the mid-gray area of the external
area.
4. The method of inserting guilloche patterns according to claim 3,
wherein the comparison between the mid-gray level of the internal
area and the mid-gray level of the external area is achieved by
Logarithmic Image Processing.
5. The method of inserting guilloche patterns according claim 1,
wherein determining the insertion intensity of the guilloche
pattern comprises selecting a thickness of the guilloche
pattern.
6. The method of inserting guilloche patterns according to claim 2,
wherein the external area is an area of pixels adjacent to the
internal area.
7. The method of inserting guilloche patterns according to claim 2,
wherein the guilloche pattern is a sinusoidal pattern, affixed
substantially horizontally to the document, the external area being
positioned vertical to the pixel of the guilloche pattern.
8. The method of inserting guilloche patterns according to claim 2,
wherein the guilloche pattern is a series of ridges corresponding
to a digital fingerprint, the internal and external areas being
positioned along a normal to the curve at the pixel in
question.
9. A device for inserting guilloche patterns into a document,
comprising a computer containing a set of instructions that prompt
said computer to implement a method for inserting guilloche
patterns in a document, each guilloche pattern being capable of
encoding variable alphanumeric data ensuring a different aspect at
each guilloche pattern so as to render said document secure, by
determining an insertion intensity of each guilloche pattern
previously generated on the basis of a mid-gray level of the
document near said guilloche pattern and in that the insertion
intensity of said guilloche pattern involves a contrast value and a
thickness of said guilloche pattern.
10. A secure document onto which are affixed guilloche patterns
encoding alphanumeric data, wherein the guilloche patterns are
inserted into the document by a method for inserting guilloche
patterns in a document, each guilloche pattern being capable of
encoding variable alphanumeric data ensuring a different aspect at
each guilloche pattern so as to render said document secure, by
determining an insertion intensity of each guilloche pattern
previously generated on the basis of a mid-gray level of the
document near said guilloche pattern and in that the insertion
intensity of said guilloche pattern involves a contrast value and a
thickness of said guilloche pattern.
11. The secure document of claim 10 wherein the secure document is
an identity document.
12. A method for extracting guilloche patterns from a secure
document likely to be degraded, the method comprising: determining
a contrast card of at least one portion of the secure document that
includes the guilloche patterns; identifying, on this contrast card
an optimal percolation trajectory; and extracting the optimal
percolation trajectory, said trajectory corresponding to the
guilloche pattern.
13. The method for extracting guilloche patterns according to claim
12, wherein the contrast card is created by means of a Logarithmic
Image Processing model.
14. The method for extracting guilloche patterns according to claim
12 or 13, characterized in that the operation of identifying the
optimal percolation trajectory involves: identifying, on the
contrast card, all of the trajectories likely to pass across the
secure document in order to connect a point of departure of a
guilloche pattern to a point of arrival of said pattern;
determining a cost function of each of the trajectories, said cost
function assessing a variability of the contrast between the
contrast determined at each point of a trajectory and an expected
contrast; comparing the cost functions of all of the trajectories;
and determining the minimal cost function, the trajectory
comprising the minimal cost function corresponding to the guilloche
pattern.
15. The method for extracting guilloche patterns according to any
of claims 12 to 14, characterized in that when the secure document
is in color, the contrast card is calculated on the basis of the
luminance image associated with the color document.
16. The method of extracting guilloche patterns, according to claim
12, further comprising: authenticating the guilloche patterns of
the secure document likely to be degraded by comparing each
extracted guilloche pattern with a corresponding theoretical
guilloche pattern.
17. The method of extracting guilloche patterns according to claim
16, wherein each guilloche pattern encodes the variable
alphanumeric data mentioned in said secure document, wherein the
theoretical guilloche pattern is obtained by Optical Character
Recognition of the alphanumeric data mentioned in the secure
document and by generating the corresponding theoretical
patterns.
18. The method of extracting guilloche patterns according to claim
16, wherein the secure document comprises an electronic chip,
wherein the theoretical guilloche pattern is an original guilloche
pattern, previously stored in the chip when generating the
guilloche pattern affixed to the secure document.
19. The method of extracting guilloche patterns according to any of
claims 16, wherein the operation of comparing the extracted and
theoretical patterns involves estimating a score based on a
distance between each point of the extracted guilloche pattern and
a corresponding point of the theoretical guilloche pattern.
20. The method of extracting guilloche patterns according to claim
19, wherein the score is calculated by accumulating the distances
for all of the points of the guilloche pattern.
21. The method of extracting guilloche patterns according to claim
19, wherein the distance is calculated on the basis of the number
of pixels.
22. The method of extracting guilloche patterns according to claim
19, wherein in that a weight is assigned to each distance, the long
distances having a greater weight than the short distances.
23. The method of extracting guilloche patterns according to claim
22, wherein the weight assigned to each distance can be
adjusted.
24. A computer containing a set of instructions that prompt said
computer to implement a method for authenticating guilloche
patterns of a secure document likely to be degraded by: determining
a contrast card of at least one portion of the secure document that
includes the guilloche patterns; identifying, on this contrast card
an optimal percolation trajectory; extracting the optimal
percolation trajectory, said trajectory corresponding to the
guilloche pattern; and authenticating the guilloche patterns of the
secure document likely to be degraded by comparing each extracted
guilloche pattern with a corresponding theoretical guilloche
pattern.
25. An identity document comprising alphanumeric data relating to
the holder and an identity photograph to which are affixed
guilloche patterns encoding the alphanumeric data, wherein the
guilloche patterns can be authenticated by determining a contrast
card of at least one portion of the secure document that includes
the guilloche patterns; identifying, on this contrast card an
optimal percolation trajectory; extracting optimal percolation
trajectory, said trajectory corresponding to the guilloche pattern;
and authenticating the guilloche patterns of the secure document
likely to be degraded by comparing each extracted guilloche pattern
with a corresponding theoretical guilloche pattern.
Description
TECHNICAL FIELD
[0001] The present invention concerns a method for inserting
guilloche patterns containing coded data and a device for inserting
said guilloche patterns. It also concerns a method for extracting
and authenticating guilloche patterns containing encoded data. It
also concerns an authentication device as well as a secure document
needing to be authenticated such as an identity card, a driving
license, a notarial deed, etc. The invention has applications in
the field of secure documents and, in particular, the
authentication of secure documents even when these are damaged.
STATE OF THE ART
[0002] In a known way, security documents, like identity documents
for example, generally comprise an identity photograph of their
holder as well as alphanumeric data such as, for example, the name
of the holder, his date of birth, his height, his address, the
document number, the date of issue of the document and/or the
identity of the authority that issued the document.
[0003] In order to render identity documents secure, it is known to
associate the identity photograph with guilloches. These guilloches
form a network of undulating lines superimposed on the photograph
and visible to the naked eye. The guilloches are intended to make
discernable, during an identity check, any fraudulent modification
of the photograph. In particular, they make it possible to defend
against changes in color of the photograph, for example when a
beard or hair is added. Thus, guilloches generally enable the
performance of level 1 (visual check with the naked eye) and/or
level 2 (visual check with a simple optical device such as a
magnifying glass or ultraviolet light) security checks.
[0004] Moreover, it is also known to implement means of protecting
the alphanumeric data mentioned in identity documents in order to
defend against alternations to these data such as, for example,
modifications of these alphanumeric references.
[0005] The protection of alphanumeric data can be achieved by
digital tattooing techniques (known as watermarking) intended to
incorporate elements invisible to the naked eye into an identity
photograph, these elements coding predefined information.
Watermarking provides level 3 security (automatic verification of
encoded data) during a security check. Thus, by means of a digital
processing and analysis device, the identity photograph is analyzed
and the data that are watermarked therein are extracted. A
verification of the consistency of these data is then
performed.
[0006] However, watermarking has a certain number of drawbacks. In
fact, since it is not visible to the naked eye, watermarking does
not enable a level 1 or 2 security check to be performed. The
verification of watermarked secure documents therefore requires
trained personnel, equipped with large means of analysis, which
limits the security checks, particularly mobile checks.
Furthermore, watermarks can be sensitive to degradations of the
identity document, degradations that can be caused, during the
period of validity of the document, by natural wear, exposure to UV
rays, lack of care by the holder, etc. The analysis of degraded
watermarks can then result in an incorrect reading of the
watermarks, or the impossibility of reading them during the
check.
[0007] Another known technique also makes it possible to render
said alphanumeric data mentioned in the identity documents secure.
This technique proposes to insert, in the identity photograph,
variable guilloches encoding all or part of the alphanumeric data.
Examples of methods of rendering documents secure by using such
variable guilloches are specifically described in patent
applications EP 2 325 022 A1 and US 2010/0260372 filed in the name
of the applicant.
[0008] These guilloches must enable the implementation of both a
level 1 and a level 3 security check. To implement a level 1
security check, the guilloches must not interfere with the visual
perception of the underlying content of the document, particularly
the photograph, and must not prevent good readability of the
characteristic traits of the holder of the secure document.
[0009] Furthermore, and in a compatible manner, the guilloches must
be sufficiently marked in order to be able to be extracted
automatically by means of an authentication device and thus meet
the requirements of security level 3. In fact, the implementation
of security level 3 requires, prior to any extraction of the
guilloches, a phase of printing the photograph onto the document
then a phase of scanning the image formed of the photograph and of
the superimposed guilloches. Now, these so-called "print-scan"
phases generate a double degradation of the quality of the image,
the degree of degradation depending in particular on the quality of
the print-scan system. An example of an original image and its
degraded images is shown in FIG. 1. In particular, image (a) in
FIG. 1 represents an example of an original digital image,
comprising a photograph of the holder of a secure document on which
guilloches are superimposed. Images (b), (c) and (d) represent the
image (a) degraded by a print-scan system of high quality, of
average quality and of low quality, respectively. In addition to
the double print-scan degradation, the secure documents tend to
undergo additional degradations during their period of validity,
such as natural wear, the effects of UV rays, physical aggressions,
etc. Also, so that the automatic extraction of the guilloches, at
security level 3, do not suffer from the degradations undergone by
the security document, it is important that these guilloches are
inserted in a sufficiently marked manner within the document.
[0010] Furthermore, in order to implement a security level 3 check,
the guilloches affixed to the photograph must be capable of being
extracted automatically by means of an authentication device so
that they can be checked and/or authenticated. A level 3
verification/authentication of a document rendered secure by
guilloches requires, prior to any extraction of the guilloches, a
phase of printing the photograph onto the document then a phase of
scanning the image formed of the photograph and the superimposed
guilloches. Now, these print-scan phases cause a double degradation
of the quality of the image, the degree of degradation depending
chiefly on the quality of the print-scan system. An example of an
original image and its degraded images is represented in FIG. 6. In
particular, image (a) of FIG. 6 represents an example of an
original digital image, comprising a photograph of the holder onto
which guilloches are superimposed. Images (g), (h) and (j)
represent image (a) degraded by a print-scan system, of high
quality, medium quality and low quality, respectively.
[0011] Furthermore, like any secure document, documents rendered
secure by guilloches undergo additional degradations during their
period of validity, such as natural wear, the effects of UV rays,
physical aggressions, etc.
[0012] The double degradation of the print-scan phase, to which can
be added additional degradations, has the effect of impeding the
extraction of the guilloches, which makes it impossible to
check/authenticate the alphanumeric data encoded in the guilloches
and compromises the implementation of level 3 security.
SUMMARY OF THE INVENTION
[0013] In order to address the above-mentioned dual problem of
readability with the naked eye of the document with guilloches and
of extraction of the guilloches when the secure document is
degraded, the applicant proposes to insert the guilloches, or
guilloche patterns, with an insertion intensity determined on the
basis of the level of mid-gray of the document near the guilloche
patterns.
[0014] In order to address the above-mentioned problem of the
impossibility of checking a document rendered secure by guilloches
when the quality of the guilloches is degraded, the applicant
proposes to extract the guilloches, or guilloche patterns, based on
trajectories generated on the basis of the contrasts of the secure
document.
[0015] According to a first aspect, the invention concerns a method
of inserting guilloche patterns in a document, each guilloche
pattern being capable of encoding variable alphanumeric data
ensuring a different aspect at each guilloche pattern so as to
render said document secure. This method is characterized in that
it comprises an operation of determining an insertion intensity of
each guilloche pattern previously generated on the basis of a
mid-gray level of the document near said guilloche pattern.
[0016] This method enables the guilloche patterns to be inserted
with an intensity that depends on the gray level of the document in
the place where the guilloche pattern is affixed. The marking of
the guilloche pattern on the document is thus more or less marked
and depends on the photographic environment.
[0017] This method can be applied to all sorts of secure documents.
It can be applied in particular: [0018] to identity documents such
as identity cards, passports, driving licenses, etc., where the
guilloche patterns are usually applied onto the holder's
photograph, [0019] to secure documents with or without a
photograph, such as civil status documents, notarial deeds (known
as "breeder documents") or mobile identity documents (known as
"mobile ID" documents), where the entire document contains
guilloche patterns, or [0020] to documents for the protection of
brands ("brand protection" documents) or other physical marking
(for example packaging and luxury goods) for which authentication
of origin is required.
[0021] Advantageously, the insertion intensity of a guilloche
pattern involves a contrast value and a thickness of said guilloche
pattern. Varying the thickness and contrast of a guilloche pattern
allows said pattern to be more or less marked on the document.
[0022] According to certain embodiments, determining the insertion
intensity of the guilloche pattern involves a calculation
operation, in each pixel of said guilloche pattern, of the contrast
value between an internal area of the guilloche pattern and an
external area near said internal area.
[0023] According to one or more embodiments, the contrast value is
obtained by comparison between the mid-gray level of the internal
area and the mid-gray area of the external area.
[0024] According to certain embodiments, the comparison between the
mid-gray level of the internal area and the mid-gray level of the
external area is achieved by Logarithmic Image Processing (or
LIP).
[0025] According to certain embodiments, determining the insertion
intensity of the guilloche pattern involves an operation of
selecting a thickness of the guilloche pattern.
[0026] According to certain embodiments, the external area is an
area of pixels adjacent to the internal area.
[0027] According to certain embodiments, the guilloche pattern is a
sinusoidal pattern, affixed substantially horizontally to the
document, the external area being positioned vertical to the pixel
or pixels of the guilloche pattern.
[0028] According to certain embodiments, the guilloche pattern is a
series of ridges corresponding to a digital fingerprint, for
example that of the holder of the document, the internal and
external areas being positioned along a normal to the curve at the
pixel in question. According to a second aspect, the invention
concerns a device for the insertion of guilloche patterns into a
document, comprising a computer containing a set of instructions
that prompt said computer to implement the method for inserting
guilloche patterns as described above. This device enables
guilloche patterns to be inserted with a more or less marked
marking depending on the photographic environment.
[0029] According to a third aspect, the invention concerns a secure
document onto which are affixed guilloche patterns encoding
alphanumeric data, characterized in that the guilloche patterns are
inserted into the document by the insertion method described
above.
[0030] According to a fourth aspect, the invention concerns an
identity document comprising an identity photograph and
alphanumeric data relating to the holder, characterized in that the
identity photograph contains in a visible manner guilloche patterns
coding the alphanumeric data, inserted by the insertion method
described above.
[0031] According to a fifth aspect, the invention concerns a method
for extracting guilloche patterns from a secure document likely to
be degraded, the method comprising the following operations: [0032]
determining a contrast card of at least one portion of the secure
document that includes guilloche patterns; [0033] identifying, on
this contrast card, an optimal percolation trajectory; and [0034]
extracting the optimal percolation trajectory, said trajectory
corresponding to the guilloche pattern.
[0035] This method allows guilloche patterns to be extracted even
when they are difficult to perceive with the naked eye. It
therefore allows guilloche patterns to be extracted from secure
documents that have undergone degradations.
[0036] This method can apply to all sorts of secure documents. It
can apply in particular: [0037] to identity documents such as
identity cards, passports, driving licenses, etc., where the
guilloche patterns are usually applied to the photograph of the
holder, [0038] to secure documents with or without a photograph,
such as civil status documents, notarial deeds (known as "breeder
documents") or mobile identity documents (known as "mobile ID"
documents), where the entire document contains guilloche patterns,
or [0039] to documents for the protection of brands ("brand
protection" documents) or other physical marking (for example
packaging and luxury goods) for which authentication of origin is
required.
[0040] Advantageously, the contrast card is created by means of a
Logarithmic Image Processing (LIP) model. This LIP model allows the
contrasts that are compatible with human vision to be
determined.
[0041] According to certain embodiments, the operation of
identifying the optimal percolation trajectory involves: [0042]
identifying, on the contrast card, all of the trajectories likely
to pass across the secure document in order to connect a point of
departure of a guilloche pattern to a point of arrival of said
pattern; [0043] determining a cost function of each of the
trajectories, said cost function assessing a variability of the
contrast between the contrast determined for each trajectory and an
expected contrast; [0044] comparing the cost functions of all of
the trajectories; and [0045] determining the minimal cost function,
the trajectory comprising the minimal cost function corresponding
to the guilloche pattern.
[0046] According to one or more embodiments, when the document and
in particular the photograph is in color, the contrast card is
calculated on the basis of the luminance image associated with the
color image.
[0047] According to a sixth aspect, the invention concerns a method
of authentication of the guilloche patterns of a secure document
likely to be degraded, this method involving: [0048] operations for
extracting the guilloche patterns previously defined, and [0049] an
operation of comparing each extracted guilloche pattern with a
corresponding theoretical guilloche pattern.
[0050] This method of authentication allows a secure document to be
checked at security level 3, even when the secure document is
damaged and/or the quality of the guilloche patterns is
degraded.
[0051] According to one or more embodiments, when each guilloche
pattern encodes the variable alphanumeric data mentioned in said
secure document, the theoretical guilloche pattern is obtained by
Optical Character Recognition (OCR) of the alphanumeric data
mentioned in the secure document and by generating the
corresponding theoretical patterns.
[0052] According to some embodiments, when the secure document
comprises an electronic chip, the theoretical guilloche pattern is
an original guilloche pattern, previously stored in the chip when
generating the guilloche pattern affixed to the secure
document.
[0053] According to one or more embodiments, the operation of
comparing the extracted and theoretical patterns involves
estimating a score based on a distance between each point of the
extracted guilloche pattern and a corresponding point of the
theoretical guilloche pattern.
[0054] According to a variation, the score is calculated by
accumulating the distances for all of the points of the guilloche
pattern.
[0055] According to certain embodiments, the distance is calculated
on the basis of the number of pixels.
[0056] According to certain embodiments, a weight is assigned to
each distance, the long distances having a greater weight than the
short distances. This weight can be adjusted.
[0057] According to a seventh aspect, the invention concerns a
device for authenticating guilloche patterns comprising a computer
containing a set of instructions that prompt said computer to
implement the above-described method for authenticating the
guilloche patterns.
[0058] According to an eighth aspect, the invention concerns an
identity document comprising alphanumeric data relating to the
holder and an identity photograph to which are affixed guilloche
patterns encoding the alphanumeric data, characterized in that the
guilloche patterns can be authenticated by the method defined
above.
BRIEF DESCRIPTION OF THE FIGURES
[0059] Further features and advantages of the invention will emerge
from reading the description, illustrated by the Figures in
which:
[0060] FIG. 1, previously described, represents an example of an
original secure document and deteriorated secure documents;
[0061] FIG. 2 represents an example of an original photograph, of
this same photograph with guilloches and of this secure photo after
printing and scanning;
[0062] FIG. 3 represents an example of a section of a guilloche
pattern from which the contrast value is calculated;
[0063] FIG. 4 represents examples of photographs with guilloche
patterns inserted according to the method of the invention and, for
each of these photographs, an example of the guilloche patterns
detected during a level 3 security check;
[0064] FIG. 5 represents a block diagram of an example of the
insertion method according to the invention;
[0065] FIG. 6, previously described, represents an example of an
original secure document and damaged secure documents;
[0066] FIG. 7 represents an example of different states of a secure
document during the extraction method according to the
invention;
[0067] FIG. 8 represents an example of an extracted guilloche
pattern and a theoretical guilloche pattern;
[0068] FIG. 9 represents examples of authenticable secure documents
and non-authenticable secure documents according to the method of
the invention;
[0069] FIG. 10 represents a block diagram of an example of the
authentication method according to the invention.
DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT
[0070] An example of an embodiment of a method for inserting
guilloche patterns in a secure document is described in detail
below, with reference to the accompanying drawings. An example of
an embodiment of a method for authenticating guilloche patterns of
a secure document, even when said secure document is degraded, is
also described in detail below, with reference to the accompanying
drawings. These examples show the features and advantages of the
invention. It should be remembered, however, that the invention is
not limited to these examples.
[0071] In the Figures, identical elements bear the same reference
numerals. For ease of readability of the Figures, no size scale
between the elements shown is observed.
[0072] The method of the invention proposes to insert guilloche
patterns such as those previously mentioned in one portion of or
over the entire secure document. In the following description, the
method will be described when it is applied to a portion of a
secure document such as a photograph on which are superimposed the
guilloche patterns, also called guilloches. In the description, the
word "photograph" shall be understood as referring indiscriminately
to a portion of secure document or an underlying content. A person
skilled in the art will also understand that the method as it will
be described can also be implemented for a document of which the
entirety of said document comprises guilloche patterns.
[0073] These guilloche patterns are, for example, one-dimensional
patterns, or 1D guilloche patterns, adapted to encode alphanumeric
data such as the personal data of the holder that are mentioned in
the identity documents. Each 1D guilloche pattern is in the form of
a variable undulating line, visible to the naked eye, on an
underlying content, and in particular on a photograph.
[0074] According to the invention, the visual prominence is of
sufficiently low intensity as not to interfere with the visual
perception of the underlying content, namely the portion of the
secure document located beneath the guilloche patterns--for example
the photograph--although it is sufficiently marked to enable an
automatic extraction even when the secure document is degraded for
reasons like those previously mentioned.
[0075] Examples of a photograph of a secure document are
represented in FIG. 2. Image (a) of this FIG. 2 represents a
digital photograph of the holder. Image (b) of this FIG. 2
represents photograph (a) to which have been affixed guilloche
patterns according to the invention. As image (b) shows, the
guilloche patterns do not impede the readability of the photograph;
in other words, the holder is recognizable to the naked eye,
despite the presence of guilloche patterns. Security level 1 is
thus ensured. Image (c) of this FIG. 2 represents an example of
image (b) when it has been damaged by a print-scan method. This
image (c) shows that, even in the presence of damage, the guilloche
patterns inserted according to the method of the invention remain
sufficiently marked as to be automatically detectable by an
authentication machine, so as to ensure security level 3.
[0076] So that the guilloche patterns are inserted into the
photograph in a sufficiently marked manner to ensure security level
3 while enabling readability of the photograph, the method of the
invention proposes that the insertion intensity of each guilloche
pattern be adapted on the basis of the gray level of the
photograph. The insertion intensity is determined, for each pixel
of the guilloche pattern, on the basis of the gray level of the
pixels of the photograph around said guilloche pattern. According
to the invention, the insertion intensity is defined by the
thickness of the guilloche pattern and by the level of contrast
between the photograph and said guilloche pattern.
[0077] In the method of the invention, the thickness is the number
of pixels aligned in the same direction (horizontal or vertical for
example) to form the guilloche pattern inserted in the
photograph.
[0078] Generally speaking, the contrast is a property of an image
that quantifies the difference in luminosity between the light and
dark parts of the image. In the method of the invention, the
contrast is the difference in luminosity between the guilloche
pattern and the area of the photograph near said guilloche pattern.
The contrast is a unitless value, calculated for each pixel of each
guilloche pattern.
[0079] In order to calculate the contrast, the method of the
invention proposes to calculate the contrast between the mid-gray
level of an area inside the guilloche pattern and the mid-gray
level of at least one area outside said guilloche pattern. FIG. 3
represents an example of a portion of photograph comprising an area
zi inside the guilloche pattern and two areas ze outside said
guilloche pattern. This portion of photograph comprises several
pixels p1-pn aligned in the same direction. The internal area zi
contains the pixels of a slice of the guilloche pattern. Each
external area ze contains pixels of the photograph, aligned with
the pixels of the internal area zi. In the example of FIG. 3,
pixels p1-pn are aligned vertically because the guilloche pattern
is a pattern having a sinusoidal shape extending in a broadly
horizontal direction, as will be described in greater detail
below.
[0080] The portion of photograph in FIG. 3 contains those of the
pixels p1-pn that form the slice of the guilloche pattern. It
comprises in particular pixel px, called the current pixel, the
contrast of which is required to be determined. These pixels of the
internal area zi constitute the thickness of the guilloche pattern.
This thickness is variable. In the example of FIG. 3, the thickness
is 5. It can also be, for example, 7 or 9, as in the examples of
FIG. 4 previously described. The thickness of the pattern as well
as the contrast--the force of insertion--are chosen on the basis of
their psycho-visual impact (the guilloches must not interfere with
the observation of the photograph) and robustness (the extraction
of guilloche patterns must function properly, even after ageing).
Furthermore, the thickness chosen is heavily dependent on the
quality of the print-scan system: the print step and the scan step
each have their own resolution (size of a pixel), usually worse
than that of the original image. This has the effect of affecting
the colors of the pixels located at the border of the guilloche
pattern: the thickness of the guilloche pattern must be sufficient
for the colors of the central pixels (near the axis of said
guilloche pattern) to be correct, in order to prepare a future
extraction.
[0081] The portion of photograph in FIG. 3 also contains external
areas ze adjacent to the internal area zi. Each of these external
areas ze contains the pixels of the photograph that are near the
internal area zi. The number of pixels of each external area ze is
predefined. In the example shown in FIG. 3, the external area ze1,
like the external area ze2, contains two pixels selected in the
continuity and alignment of the pixels of the internal area zi.
Thus, the pixels of the external areas ze1, ze2 and of the internal
area zi are aligned in the same direction. In the example in FIG.
3, the pixels of the external [areas] ze1 and ze2 are aligned
vertically with the pixels of the internal area zi, above and below
the internal area zi respectively, so that the guilloche pattern is
broadly horizontal.
[0082] In fact, a person skilled in the art will understand that if
the guilloche pattern is affixed in a horizontal direction on the
photograph, a slice of said guilloche pattern contains vertically
aligned pixels; the internal and external areas are then aligned
vertically, as in the example shown in FIG. 3. By contrast, if the
guilloche pattern is affixed in a vertical direction on the
photograph, then the slice of said guilloche pattern contains
horizontally aligned pixels; the internal and external areas are
then aligned horizontally.
[0083] In certain embodiments, the guilloche pattern is a
sinusoidal pattern, extending across the photograph horizontally or
vertically, or even slanting. If the guilloche pattern is
sinusoidal, the direction of said pattern is the overall crossing
direction of the photograph.
[0084] In certain embodiments, the guilloche pattern can consist of
ridges of an imprint, for example a fingerprint of the holder. In
this case, the internal and external areas are positioned along a
normal to the curve at the point in question, i.e. orthogonally to
an estimated tangent direction near said point.
[0085] According to the invention, the contrast is calculated for
each pixel of the internal area zi by comparing the mid-gray level
of the internal area zi and the mid-gray level of the external
areas ze. In the case of a color image, the mid-gray level is
determined from the luminance image associated with the color
image.
[0086] The comparison between the mid-gray level of the internal
zone and the mid-gray level of the external zone is achieved by
Logarithmic Image Processing (LIP), which is described, for
example, in the publication by M. Jourlin and J-C. Pinoli, "A Model
for Logarithmic Image Processing," Journal of Microscopy, 149 (1),
pages 21-35, 1988 or in the publication by M. Jourlin, "Logarithmic
Image Processing: Theory and Applications," Advances in Imaging and
Electron Physics, Vol. 195, 253 p. 2016.
[0087] Thus, in each pixel of the guilloche pattern, a contrast
value is calculated that is added to or subtracted from the image
by LIP so as to obtain an additional LIP contrast chosen from the
mid-gray levels of the internal area zi and external areas ze. The
same contrast value will then be applied to all the points of the
internal area zi. Thus the pixels of the same slice of guilloche
pattern all have the same contrast value. However, the guilloche
pattern can have a contrast value that varies from one slice to
another. In other words, the same guilloche pattern can have a
contrast that varies along its length. In the example shown in FIG.
2, the guilloche patterns can be more marked in the area of the
person's hair than in the background areas of the image.
[0088] FIG. 4 shows several examples of the same photograph to
which are affixed guilloche patterns of different insertion
intensity. Although this intensity can vary from one guilloche
pattern to another, in the examples in FIG. 4 an identical
insertion intensity of the guilloche patterns is chosen for all of
the patterns of the same image. In these examples in FIG. 4, the
insertion intensity differs from one image to the other. Images
(a1), (b1) and (c1) are images, after print-scan, of the same
holder. The guilloche patterns of image (a1) have a thickness of 5,
which corresponds to a slice of guilloche pattern of 5 pixels
aligned vertically. The guilloche patterns of image (b1) have a
thickness of 7 and the guilloche patterns of image (c1) have a
thickness of 9. The contrast value of each of these examples has
been determined as the thicknesses, based on the quality of the
print-scan system: a stronger contrast makes for an easier
extraction. It will be seen that, since the guilloche patterns are
inserted more intensely in image (c1) than image (a1), the person
in image (c1) is clearly recognizable to the naked eye.
[0089] Images (a2), (b2) and (c2) in FIGS. 4 are images after
automatic detection of the guilloche patterns during a level 3
check. The guilloches visible in figures (a2), (b2) and (c2) are
the guilloches detected (reconstructed) by the authentication
machine during a level 3 check. It can be seen that, although the
guilloche patterns are inserted less intensely in image (a1) than
image (c1), the respective images (a2) and (c2) show that the
detection of the guilloche patterns gives as good results with the
guilloche patterns of image (a1) as with those of image (c1).
[0090] FIG. 5 represents an example of a block diagram showing the
different steps of the insertion method according to the invention.
This method comprises a first step 100 of generation of a guilloche
pattern. The guilloche pattern is a curve derived from a function,
for example a sinusoidal function, that encodes alphanumeric data.
Numerous documents describe methods for the generation of
guilloches. The generation of guilloche patterns will not,
therefore, be described in this application.
[0091] The guilloche patterns generated are then positioned--step
200--on the photograph (or other document) with a predefined
spacing that depends, for example, on the number of guilloche
patterns to be affixed and/or the amount of modulation used during
the generation of the guilloche patterns.
[0092] The method then involves step 300 of selection and
application of a guilloche thickness. When the guilloche is
generated and its thickness has been defined, a step 400 of
calculation of the contrast value is performed for each pixel of
the guilloche. Operation 400 of calculation of the contrast value
is repeated for the next n pixel (steps 410 and 420) until all of
the N pixels of the guilloche pattern have been processed.
[0093] When the contrast value is determined, the guilloche is
inserted in the document at step 500. The method is repeated from
step 300 of application of the thickness for the next k guilloche
until all of the K guilloches have been inserted in the document
(steps 510 and 520). When all of the guilloches have been inserted
(step 510), the document is secure (step 600).
[0094] The contrast value determined, associated with the chosen
thickness of the guilloche pattern, constitutes the insertion
intensity of a guilloche. The insertion intensity enables a more or
less intense marking of each guilloche pattern, which directly
depends on the gray level of the document onto which it is affixed.
The intensity of marking is therefore directly dependent on the
gray level of the document near the guilloche. This allows the
underlying content to be readable with the naked eye, whatever the
state of the document, and the guilloche patterns can be detected
and the encoded data authenticated.
[0095] The insertion method as it has just been described can be
implemented in a device for the insertion of guilloche patterns in
a document. This device comprises at least one computer performing
a set of instructions that prompts said computer to implement this
guilloche insertion method.
[0096] The method of the invention proposes to authenticate the
guilloche patterns inserted in a portion or in the entirety of a
secure document such as those previously mentioned. In the
description that follows, the method will be described when it is
applied to a portion of a secure document such as a photograph onto
which are superimposed guilloche patterns, also called guilloches.
A person skilled in the art will understand that the method as it
will be described can also be implemented for a document of which
the entirety of said document comprises guilloche patterns. These
guilloche patterns are, for example, one-dimensional patterns, or
1D guilloche patterns, adapted to encode alphanumeric data such as
the personal data of the holder, mentioned in identity documents.
Each 1D guilloche pattern is in the form of a variable undulating
line, visible to the naked eye, on an underlying content, and in
particular on a photograph, but of which the visual prominence is
of sufficiently low intensity as not to interfere with the visual
perception of the underlying content, namely the portion of the
secure document located beneath the guilloche patterns.
[0097] An example of a document rendered secure by guilloche
patterns 601-608 is represented in image (a) of FIG. 7. In this
example, the portion 600 of the secure document is a photograph
onto which are superimposed 1D guilloche patterns, referenced
601-608. As the secure document 600 shows, the guilloche patterns
601-608 are a series of undulating and irregular lines, the
irregularities of which correspond to coded data. The guilloche
patterns 601-608 differ from one another. They are all slightly
prominent, which makes it possible not to visually interfere with
the main traits of the person in the photograph 600. In other
words, the prominence of the guilloche patterns on the underlying
content is limited so that the attention of the checker is not
focused on the patterns but on said underlying content.
[0098] In the rest of the description, the underlying content onto
which the guilloche patterns are affixed will be called
indiscriminately photograph, underlying content or image (a).
[0099] An example of the authentication method according to the
invention is represented in FIG. 10. This method comprises several
operations 710-730 enabling the guilloche patterns to be extracted
from the scanned secure document 600. In fact, as previously
explained, level 3 security requires, before implementing the
authentication method, a print-scan phase of the secure document.
Now, this print-scan phase degrades the quality of the information
contained in the secure documents, and in particular that of the
photograph and guilloche patterns. An example of a photograph with
original guilloches, called image (a), and of the same photograph
with guilloches after degradation by the print-scan phase, called
image (b), are represented in FIG. 7. As the comparison between
images (a) and (b) shows, the guilloche patterns of image (b) are
substantially degraded compared to those of image (a), which makes
the automatic extraction of these guilloche patterns more complex.
In order to extract the guilloche patterns of image (b), it is
therefore necessary to perform the series of operations described
below.
[0100] Firstly, the extraction method according to the invention
comprises an operation 710 of determination of a contrast card of
the portion 600 of the secure document. This operation, which
serves to reveal the contrasts along the guilloche patterns of
image (b), comprises a calculation, at each point of each guilloche
pattern, of the contrast between the mid-gray level of an internal
area and the mid-gray level of an external area of said point. The
internal area of the guilloche pattern is defined as the vertical
neighborhood of the pixel in question, with a predetermined
thickness, for example of two pixels, on either side of said pixel.
The external area of the guilloche pattern is defined as the
vertical neighborhood around the internal area, with a
predetermined thickness, for example of four pixels, around said
internal area.
[0101] Calculation of the contrast, according to certain
embodiments, is based on LIP (Logarithmic Image Processing)
described, for example, in the publication of M. Jourlin and J-C.
Pinoli, "A Model for Logarithmic Image Processing," Journal of
Microscopy, 149 (1), pages 21-35, 1988 or in the publication of M.
Jourlin, "Logarithmic Image Processing: Theory and Applications,"
Advances in Imaging and Electron Physics, Vol. 195, 253 p. 2016.
The general principle of this calculation of the contrast is that,
in each pixel of the guilloche pattern, the supplementary LIP
contrast chosen between the mid-gray values of the internal area of
the guilloche pattern and the external area is calculated.
[0102] The calculation of the contrast at each point of the
guilloche patterns enables a contrast card to be created, as
represented by image (c) of FIG. 7.
[0103] When the document, and particularly the photograph, is in
color, the contrast card is calculated on the basis of the
luminance image associated with the color image. For this, a
luminance image (in gray levels) calculated on the basis of the
three color planes is extracted beforehand.
[0104] The extraction method then involves an identification
operation 720, on this contrast card, of the optimal percolation
trajectory. According to certain embodiments, this operation 720
involves an identification of all of the percolation trajectories
likely to cross the image (c) in order to connect a point of
departure of a guilloche pattern to a point of arrival of said
guilloche pattern. In fact, the 1D guilloche patterns are
positioned, in the secure document, according to a horizontal
overall direction. Each guilloche pattern therefore crosses the
image from one side to the other, from left to right. The method
then proposes to find, within the contrast image (c), all of the
trajectories that cross the image from left to right. A person
skilled in the art will understand that in the case where the
guilloche patterns have a non-horizontal overall direction, for
example vertical or slanting, the points of departure and the
points of arrival of the percolation trajectories sought are not
necessarily on the left and right of the image but, for example, at
the top and bottom of the image.
[0105] The method then proposes to determine, among all of the
detected percolation trajectories, the optimal percolation
trajectory, i.e. the trajectory that has the most preferred
direction. This detection of the optimal percolation trajectory is
achieved by calculating a cost function for each of the
trajectories and by determining the minimal cost function. The cost
function of a trajectory corresponds to the variability of the
contrast between the contrast determined for each trajectory and an
expected contrast, previously determined. The closer the contrast
to the expected contrast, the lower the cost function. The cost
function therefore favors points that have contrast levels near the
contrast value chosen for the insertion of the guilloche pattern
into the secure document. The optimal percolation trajectory is
therefore, among all the detected percolation trajectories, the one
that has the smallest cost function.
[0106] According to the method, this optimal percolation trajectory
is deemed to be the guilloche pattern. The guilloche pattern is
then extracted (step 730 of FIG. 10) once the optimal percolation
trajectory has been determined. In the example of FIG. 7, image (d)
shows the optimal percolation trajectories, i.e. the guilloche
patterns 611-618 resulting from the contrast image (c). A
comparison of image (d) with image (a) of FIG. 7 shows that the
guilloche patterns 611-618 extracted with the method previously
described--image (d) --are close to the original guilloche patterns
601-608 of image (a). These extracted guilloche patterns 611-618,
although resulting from an image (b) where they are barely visible,
can be used at security level 3. An authentication of these
guilloche patterns can then be implemented.
[0107] The authentication method according to the invention
comprises an operation 740 of comparison of each extracted
guilloche pattern with the corresponding theoretical guilloche
pattern. According to certain embodiments, the theoretical
guilloche pattern is the original guilloche pattern, i.e. the one
that was generated initially and affixed onto the content of the
document to be rendered secure. At the moment of authentication of
the guilloche pattern, the extracted guilloche pattern (for example
pattern 618) is compared to the corresponding guilloche pattern
that is stored in the chip (for example pattern 608). The
comparison of each of the extracted guilloche patterns with the
original guilloche patterns makes it possible to determine whether
the secure document has been forged.
[0108] In other embodiments, the theoretical guilloche pattern is
obtained by means of optical character recognition (OCR), achieved
for example during scanning of the secure document. In these
embodiments, the alphanumeric data mentioned in the secure document
alongside the image (a) are determined by optical recognition and
theoretical guilloche patterns are generated on the basis of these
recognized alphanumeric data. The extracted guilloche patterns are
then compared to these theoretical guilloche patterns and their
comparison makes it possible to determine whether the secure
document has been forged.
[0109] Whatever the technique used to obtain theoretical guilloche
patterns, the extracted guilloche patterns are compared with the
theoretical guilloche patterns, for example by superimposing said
extracted patterns and said theoretical patterns. This comparison
can be based on an estimation of a score calculated for each pair
of guilloche patterns, a pair consisting of one extracted guilloche
pattern and one theoretical pattern. This operation of estimating
the score, referenced 741 in FIG. 10, can be achieved by
calculating, at each point of the x-axis (when the guilloche
patterns extend horizontally), the distance separating the
extracted guilloche pattern and the theoretical guilloche pattern.
Thus, in an XY coordinate system, the score at a point x of the X
axis corresponds to the distance along the Y axis between the
extracted guilloche pattern and the theoretical guilloche pattern.
This distance is preferably calculated in number of pixels. An
example of calculation of the score at a point x is represented in
FIG. 8. In this example, at point x of the X axis, the
distance--referenced d--separating the extracted guilloche pattern
618 from the theoretical guilloche pattern 608 is the length along
axis Y between the two patterns 608 and 618. The scores calculated
at each point of the X axis, for a pair of guilloche patterns, are
added together to constitute the score of the extracted guilloche
pattern. The lower the score, the closer the extracted guilloche
pattern to the theoretical guilloche pattern. In FIG. 10, the
comparison of the score with a predetermined threshold is
represented by step 742. Below a predefined score threshold, the
guilloche pattern is considered to be authenticated (block 780 of
FIG. 10). Above the predefined score threshold, the guilloche
pattern is considered as not authenticated (block 790 of FIG.
10).
[0110] The scores of all of the pairs of guilloche patterns can
also be added together to authenticate or not authenticate the
secure document as a whole. Two examples of images (b) after
print-scan are shown in FIG. 9, each of these images (b) being
associated with an example of an authenticated image (e) and an
example of a non-authenticated image (f). Each of the images (e)
and (f) contain, superimposed on the photograph, the theoretical
guilloche patterns completed by the distances between the extracted
and theoretical guilloche patterns. This distance is symbolized by
the thickness of the guilloche line. In the case of images (e), the
lines representing the guilloche patterns are not very thick. The
aggregate score is below or equal to the predetermined threshold.
Image (e) is authenticated. By contrast, on the images (f), the
lines representing the guilloche patterns are thick for a
considerable length of each pattern. The aggregate score exceeds
the predetermined threshold. Image (f) is not authenticated.
[0111] In certain embodiments, a weight is assigned to each score
before being totaled. In fact, as the extraction is not usually
perfect, it is normal that small distances exist between the two
patterns of the same pair of guilloche patterns, as is the case in
the example of images (e) of FIG. 9. By contrast, when the
distances are long, as in the example of images (f) of FIG. 9,
forgery is suspected. The method therefore proposes to assign a
bigger weighting to long distances than to short distances so as to
optimize the aggregate score. A "long distance" is a distance
between one point of an extracted guilloche pattern and the
corresponding point (for example on the same axis) of the
theoretical guilloche pattern, which generates an excess thickness
of the guilloche. By contrast, a "short distance" does not cause
excess thickness in the guilloche.
[0112] It is in this way that, in certain variations, the points
assigned to the scores can be adjustable. For example, they can be
proportional to the square of the distance, to its exponential,
etc. such as to maximize the aggregate score and make forged
guilloche patterns easier to detect.
[0113] Although described through a certain number of examples,
variations and embodiments, the method of insertion of guilloche
patterns according to the invention comprises different variations,
modifications and improvements that will appear clear to a person
skilled in the art, it being understood that these variations,
modifications and improvements form part of the scope of the
invention.
[0114] Although described through a certain number of examples,
variations and embodiments, the methods of extraction and
authentication of guilloche patterns according to the invention
comprise different variations, modifications and improvements that
will appear clear to a person skilled in the art, it being
understood that these variations, modifications and improvements
form part of the scope of the invention.
* * * * *